1. Field of the Invention
The present invention relates to an inter-pressing-machine work transfer device.
2. Description of Related Art
As a work transfer device for transferring a machining material (work) between a plurality of pressing machines sequentially arranged (tandem press), there have been known robot arm type and feeder type transfer devices.
The robot arm type transfer device includes an arm turning around a pivot provided in the upright state at an intermediate position between adjoining pressing machines, and a work holder attached to a tip of the arm. With the transfer device as described above, a work can be transferred from one press to another press, when the work is held by one press, by turning the arm by about 180 degrees around the pivot (Refer to Japanese Patent Laid-Open Publication No. HEI 10-137997).
The feeder type transfer device is used in a transfer press, and includes a lift beam provided in parallel to the work transfer direction (feed direction), a carrier supported by this lift beam, and a linear motor as a feed driving unit for driving the carrier along the lift beam. With the transfer device, in the state where the work is held by a work holder supported between a pair of carriers, when the carriers are driven in the feed direction, the work can be transferred to the next machining stage (Refer to Japanese Patent Laid-Open Publication No. 2002-307116).
A transfer device used in a transfer press is described above, but the same structure can be applied also to a transfer device in a tandem press.
However, in the case of the robot arm type transfer device described above, a work is carried by turning the arm around the pivot, some specific measures are required such as widening a distance between uprights according to turning trajectories of the arm and the work.
Further in the case of the feeder type transfer device described above, interference between the lift beam arranged along the work transfer direction and a slide of a pressing machine must be prevented, namely a space for arranging a lift beam between the slide of a pressing machine and the upright is required.
Because of the features, in any of the conventional work transfer devices as described above, any upright must be provided in the upright state at a position outer from a center of the press, and size of the entire press as a line such as a tandem press including a plurality of pressing machines will become disadvantageously larger.
Recently pressing machines already having been installed are often retrofitted, and there are the strong needs for development of a work transfer device which can advantageously be used in retrofitting the existing pressing machines. Especially in a device for pressing already having been installed, sometimes a distance between the adjoining pressing machines is large. When it is tried to respond to the situation where the distance between pressing machines is large, the problems as described below will be encountered.
The feed type transfer device as described above can hardly be applied, because of the specific structure, in the case where the distance between adjoining pressing machines is large.
In a case of the robot arm type work transfer device described above, it is possible to take countermeasures in retrofitting by prolonging the length of the arm between joints in proportion to a distance between adjoining pressing machines and also by raising a power of a drive unit used in each joint section. However, when an arm length of a robot arm type work transfer device is made larger or an output power of a driving unit is raised, the size of the work transfer device as a whole becomes accumulatively larger, which is disadvantageous. Further when a distance between adjoining pressing machines is small, it is extremely difficult to set a trajectory of a work evading interference with the upright or the like, which is also disadvantageous.
There has been known a work transfer device based on the loader/unloader system as a work transfer device capable of accommodating even the situation in which a distance between adjoining pressing machines is large.
In the work transfer device based on the loader/unloader system, a loader and an unloader each having the link structure are provided in the upstream side face and in the downstream side face of each pressing machine respectively, and a shuttle chassis is provided between the unloader in the upstream side and the loader in the downstream side, so that a work can be carried out from and into a main body of the pressing machine by the unloader and the loader respectively and the work is transferred to the next machining step with the shuttle chassis.
Even with the work transfer device based on the loader/unloader system as described above, when a distance between adjoining pressing machines is large, it is necessary to provide the shuttle chassis between the adjoining pressing machines in the spanning state, so that size of the device as a whole becomes larger and a large space is required for installation of the device. Further a work is delivered to or from the shuttle chassis, so that a carriage mistake easily occurs.
As described above, the size inevitably becomes larger in configuration of any type of work transfer device, and therefore it is difficult to raise the handling speed for improving the production efficiency.
To solve the problems as described above, the present applicant has proposed a work transfer device having a relatively slim configuration and allowing a higher work transfer speed (Refer to Japanese Patent Laid-Open Publication No. 2003-200231).
In this work transfer device 300, as shown in FIG. 28A and FIG. 28B, a lift beam 301 is provided in parallel to the work transfer direction T, and a carrier 302 and a sub carrier 303 each movable along the longitudinal direction of the lift beam 301 are provided, and further the work transfer device 300 includes a cross bar 305 having a vacuum cup 304 as a work holder between a pair of sub carriers 303 adjoining to each other respectively at the left and right sides.
In this work transfer device 300, the vacuum cup 304 is moved up and down via the carrier 302, sub carrier 303, and cross bar 305 by driving the lift beam 301 up and down with a lift shaft servo motor 306. Further the carrier 302 is moved along the longitudinal direction of the lift beam 301 when driven by a linear motor (not shown) provided, between the lift beam 301 and the carrier 302, and further by offsetting the sub carrier 303 in the moving direction of the carrier 302 when driven by a linear motor (not shown) provided between the carrier 302 and the sub carrier 303, the cross bar 305 and the vacuum cup 304 is moved in the work transfer direction T. Thus, by controlling positions of the two orthogonal driving shafts for movements in the vertical direction and/or in the work transfer direction T, a trajectory of movement of the vacuum cup 304, namely a transfer trajectory of a work W can be controlled.
However, in the work transfer device 300 as described above, rigidity of the lift beam 301 must be raised for insuring precision in positioning, and therefore weight of the lift beam 301 inevitably increases. Further for moving the cross bar 305 up and down, it is necessary to move the entire lift beam 301 up and down.
Because of the features, also in the work transfer device 300, size of the servo motor 306 becomes larger, so that the entire device becomes larger, which inevitably causes cost increase. When a small size servo motor is employed as the servo motor 306 to evade the problems as described above, it is difficult to raise the work transfer speed, so that the production efficiency can not be improved to a desired level, which is disadvantageous.
Further as an end section of the lift beam 301 is provided in a carrying-in/carrying-out area of a die, so that, when the die is exchanged with a new one, the operation for exchanging the die must be carried out after the lift beam 301 is moved up to outside of the carrying-in/carrying-out area, which disadvantageously causes a drop of the production yield.
As described above, there has been the strong need for development of a work transfer device for transferring a work between pressing machines allowing size reduction of the pressing device and the pressing line even when a distance between pressing machines is large like in the conventional type of pressing device.